1. Field of the Invention
The present invention relates to an electronic still camera and, more particularly, to high-speed continuous shooting suitable for the electronic still camera.
2. Description of the Related Art
An electronic still camera (also called the still video camera) has conventionally been provided with a continuous shooting mode, and the electronic shutter function of an image sensor such as a CCD has been utilized to increase the continuous shooting speed of the electronic still camera. As compared with a silver-salt camera, such a continuous shooting function is useful for the electronic still camera which uses an erasable and re-recordable medium.
To gain the continuous shooting speed, various proposals have been made. A primary factor which determines the continuous shooting speed is the operating time of mechanisms. The continuous shooting speed is not affected by the shutter of the electronic still camera since an electronic shutter is utilized. However, since a magnetic head is mechanically arranged, the time required to move the magnetic head influences the continuous shooting speed.
To solve the problem, it has been proposed to provide an electronic still camera having an image memory.
In such an electronic still camera, image data read from an image sensor are thinned out to prepare image data having a data size reduced to {fraction (1/16)} or {fraction (1/25)} of the original data size, and the thus-prepared image data are stored in the image memory so that the image data are sequentially subjected to continuous shooting. A series of data which has been prepared in this manner is read from the image memory and written to a video floppy disk. At this time, since a 1V (vertical scanning) period is necessarily needed to complete a reading from the image sensor, the 1V period constitutes a primary factor which determines the continuous shooting speed.
Regarding the high-speed continuous shooting, the above-described electronic still camera has the problems described in the following paragraphs (1) to (3).
(1) Since the 1V period ({fraction (1/60)} second) is required to complete a reading from the image sensor, it is difficult to shoot a rapidly moving subject.
(2) Even while a subject is not moving, recording is performed, so that a number of useless exposures are produced.
(3) If a plurality of exposures which have been recorded as one picture are reproduced, the motion of a subject is difficult to grasp.
An object of the present invention which has been made in the light of the above-described problems is to provide an electronic still camera which is capable of effecting continuous shooting at a far higher speed, which does not produce a large number of useless exposures during recording, and which is capable of reproducing an image so that the motion of a subject can be easily grasped.
To achieve the above-described object, according to several aspects of the present invention, there is provided an electronic still camera which is arranged as described in the following paragraphs (1), (2) and (3).
(1) In accordance with one aspect of the present invention, there is provided an electronic still camera which comprises an image sensor which allows each of its horizontal lines to be individually specified so that a video signal contained in each specified horizontal line can be read, memory means for storing the video signal read from the image sensor, selecting means for selecting a high-speed continuous shooting mode, and controlling means for executing, when the high-speed continuous shooting mode is selected by the selecting means, control to effect a high-speed reading for reading the video signal from the image sensor by thinning out the horizontal lines of the image sensor, and to cause the memory means to store video signals for a plurality of pictures obtained by the high-speed reading.
(2) In accordance with another aspect of the present invention, there is provided an electronic still camera which comprises an image sensor which allows each of its horizontal lines to be individually specified so that a video signal contained in each specified horizontal line can be read, memory means for storing the video signal read from the image sensor, selecting means for selecting a high-speed continuous shooting mode, decision means for comparing a video signal for one picture which has been read from the image sensor with a video signal for one picture which was immediately previously stored in the memory means, and determining whether both of the video signals represent a substantially identical image, and controlling means for executing, when the high-speed continuous shooting mode is selected by the selecting means, control to effect a high-speed reading for reading the video signal from the image sensor by sampling the horizontal lines of the image sensor, and, if the decision means determines that a read picture is substantially identical to a picture immediately previously stored in the memory means, to discard a video signal indicative of the read picture.
(3) In accordance with another aspect of the present invention, the electronic still camera described in the above paragraph (1) or (2) further comprises reproducing means for reproducing a series of pictures, which are stored with the high-speed continuous mode selected, so that the pictures are reproduced at predetermined time intervals one at a time.
According to the arrangements described in the above paragraphs (1), (2) and (3), if the high-speed continuous shooting mode is selected, during reading from the image sensor, the horizontal lines are thinned out and high-speed reading is performed. According to the arrangements described in the above paragraphs (2) and (3), while the high-speed continuous shooting mode is selected, if a subject does not move, a video signal read from the image sensor is discarded. According to the arrangement described in the above paragraph (3), pictures which are recorded in the high-speed continuous mode are reproduced at predetermined time intervals one at a time.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment of the present invention, taken in conjunction with the accompanying drawings.